Hydraulic Calculation for two types of hazards in a bUilding 2

[Uprof]

Hello All,

I am working on a 4 story office building located in New York City. Building consists of two (2) types of hazards one is light and other one is ordinary hazard. I am trying to size a fire pump by using hydraulic calculation for both types of hazard,

Light hazard is located on fourth floor while ordinary hazard is located on first floor. Both hazards were calculated separately and got the results with high head (60 psi) and low gpm for light hazard and low head (45 psi) and High Gpm for ordinary hazard.

My question is how can we select or which one to choose for fire pump flow and head if we have two hazards in a building and hazards are at different floors.

or else can we take highest head (60 psi from light hazard) and use this value as a source for ordinary hazard gpm calculation and then Select higher gpm from both hazards.

Thank you

 

[TravisMack]

Do you have some one in the office that can mentor you on this stuff? I only ask because this is very basic and common stuff that those of us doing this every day see all the time.

You size your pump capacity (flow rate) based on the highest demanding flow. You choose the pump rating (pressure) based on the highest demanding pressure as you state at the end of your post.

Please continue to post questions in here. This is a decent forum with a lot of knowledgeable fire protection people.


Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

"Follow" us at

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[Uprof]

Thanks for your Information. I am new to Fire protection design and no one available in my Office to check?

I have couple of questions:

Individual Calculation:

Light Hazard (Located on Fourth Floor) : 420 gpm (including 100 gpm hose stream allowance) and 60 psi head to get minimum 7 psi pressure from farthest sprinkler
Ordinary Hazard (Located on First Floor): 475 Gpm (including 250 gpm hose stream allowance) and 45 psi head to get minimum 7 psi pressure from farthest sprinkler

As you mentioned ,If I choose highest head and gpm, the pump flow and head will be 500 gpm with 60 psi head. Is this the right way to select?

or else I can choose highest head 60 psi as a source to calculate ordinary hazard gpm, in this scenario I am getting 620 gpm and furthest sprinkler psi as 26 psi than calculated (475 gpm)individually with 7 psi as minimum pressure.

am I missing anything here?.

 

[TravisMack]

First soapbox time: Fire sprinkler systems are a life safety and property protection system. Are you qualified to be dealing with these types of systems when real lives and real property are at stake? With that being said:

7 psi is the MINIMUM pressure for a sprinkler. The formula to start with is Q=k*P^0.5. You also have to go with Area per sprinkler (As) = SxL for sprinklers. Q(min) is the As * density. Now that you have that, are you really good with 7 psi for your sprinklers?

Let's say sprinkler in a typical office may be 14'x14' in an open area. That is 196 sq ft, or 19.6 gpm or 12.25 psi. That is almost double your minimum pressure of 7 psi you are trying to achieve. Even better, let's go with your ordinary hazard areas: 10'x12' spacing = 120 sq ft = 24 gpm = 18.4 psi. Why again are you working with 7 psi?

Is this supplied by a pump/tank or are you connected to a city supply? If a tank, how are you sizing your tank? If connected to a city supply, have you evaluated what pressures/flows are available from the city supply.

Please, seek the help of a mentor for fire protection system design, or just hire it out to a competent person. It seems that you may be quite lacking in the very basic understanding of fire sprinkler system design. Working with a good mentor for 5-10 years should make you quite the competent fire protection system design professional.




Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

"Follow" us at

https://www.facebook.com/pages/MFP-Design-LLC/92218417692

 

[MatthewJWillis]

You asked, "am i missing anything here?"

The answer is , everything.

Are you acting as the Engineer of record? Or as a Sprinkler System Designer?

As Travis has stated, your basic starting points are Way out.
Just looking at you numbers provided.., 420gpm for a Light hazard? Then only 55gpm more for ordinary?
Even calculating the base 1500 square feet will only net 150gpm nominal. Your number indicates a build back of 3. Whereas normal Build back is anywhere from 1.25-1.35.

Please put down your pencil.
I am sure your intentions are good, however, people can die if not done correctly.
Not meaning to sound dramatic, but even if the people get out, firefighters still come into these building and rely on the system to protect/assist them.

If you are sizing the pump for bid documents, the bids will be all over the place and the "winning" contractor will have to fix all your mistakes.

 

[chicopee]

My course of action would be to contact your fire insurance carrier since such company have dedicated fire protection engineers who ultimately will require a copy of your work for their approval in order to get discount on the cost of insurance. If your work is not to their standard, they'll recommend corrective measures which could be very expensive.

 

[SprinklerLifer]

Another issue to consider, this building is four levels. It probably will require at least one standpipe. Will the fire pump be the sole source of water for the standpipe (automatic wet)? or will there be assistance by the responding fire department (manual wet)? If the pump is supplying the standpipe(s) you're looking at a minimum 500 GPM pump with 100 PSI at the top of the standpipe. I am in agreement here with everyone else, seek a professional and competent fire protection designer.